Heat treatment of yarns

ABSTRACT

A process and apparatus for the uniform heat treatment of yarns wherein a yarn is entrained in a stream of air and is passed therewith into a central passageway of a burner leaving the outlet of the central passageway at a point where the air and a combustible fluid, which is separately supplied to the burner through a surrounding passageway terminating at the same point, meet and are ignited the yarn continuing to move in an axial direction through the combustion flame.

United States Patent Coats et al.

[ Dec. 5, 1972 [541 HEAT TREATMENT OF YARNS [72] Inventors: Robert Reid Coats; John Michael Greenway, both of Harrogate, En-

gland [73] Assignee: Imperial Chemical Industries Limited, London, England 22 Filed: March 13, -1970 [21] Appl. No.: 19,344

[30] Foreign Application Priority Data March 21, 1969 Great Britain 15,009/69 [52] US. Cl ..28/1.2, 28/63 [51] Int. Cl. ..D02j 3/16, D02g 1/00 [58] Field of Search ..28/1.4, 1.2, 1.3, 62, 63, 72.1

[56] References Cited UNITED STATES PATENTS 3,410,072 11/1968 Nimtz et a1. ..28/63 X FOREIGN PATENTS OR APPLICATIONS 529,253 9/1921 France... ..28/63 Primary ExaminerHenry S. Jaudon Attorney-Cushman, Darby & Cushman ABSTRACT A process and apparatus for the uniform heat treatment of yarns wherein a yarn is entrained in a stream of air and is passed therewith into a central passageway of a burner leaving the outlet of the central passageway at a point where the air and a combustible fluid, which is separately supplied to the burner through a surrounding passageway terminating at the same point, meet and are ignited the yarn continuing to move in an axial direction through the combustion flame.

6 Claims, 2 Drawing Figures HEAT TREATMENT OF YARNS This invention relates to the heat treatment of yarns and in particular to uniform heat treatment by means of a flame.

According to the present invention we provide a process for the uniform heat treatment of yarns wherein a yarn is entrained in a stream of air and is passed therewith into a central passageway of a burner leaving the outlet of the central passageway at a point where the air and a combustible fluid, which is separately supplied to the burner through a surrounding passageway terminating at the same point, meet and are ignited the yarn continuing to move in an axial direction through the combustion flame.

In U.K. patent specification 1,179,734 is described a process for heat treating a travelling yarn wherein the yarn is led through a gas burner in its passage between feed and withdrawal rolls. In a process according to this invention an advantage is obtained by carrying a yarn through a burner with a stream of combustion air in that by this means greater control of relaxation may be effected. Improved stability of operation appears to result, at least in part, from dispensing with the burner casing which surrounds the flame and the relaxing yarn for part of its travel in the method of specification 1,179,734.

A process according to the invention may be used for the heat treatment of any kind of textile yarn, as for example, continuous filament or staple fiber yarns composed of a synthetic thermoplastic polymer, or a staple fiber yarn composed of natural fibers or mixtures of synthetic and natural fibers. The invention is particularly suitable for treating yarns composed of or containing thermoplastic fibers or filaments by reason of the uniformity of heat treatment which is achieved. The invention may also be used for the uniform surface treatment of yarns, particularly natural fiber yarns which require the removal of protruding fiber ends by charring.

A simple air ejector may most conveniently be used to entrain a yarn in a stream of air. The ejector may have any one of several forms. One such form comprises a yarn entry passageway of narrow bore into which yarn is drawn by the suction developed therein by entry into the passageway of air under pressure downstream of the point of entry of the yarn, said air proceeding through the passageway in a generally downstream direction. An air pressure is used such as to provide the required tension to draw the yarn from a supply means into the yarn passageway and forward it to the combustion zone.

In another form of ejector a yarn entry tube or passageway which is quite short is surrounded at its lower end by the open end of a slightly larger tube. The junction of the two tubes is enclosed in a chamber to which air under pressure is supplied. The air enters the larger tube through the space between the two tubes and in passing through the larger tube induces a reduced pressure in the yarn passageway which draws a yarn thereinto tensioning and forwarding it through the larger tube to the combustion zone.

Whatever form of ejector is used it must provide sufficient tension in the yarn to draw it from the source of yarn at a sufficiently high speed but without the need for an air flow greater than is required to support combustion of the combustible fluid. It is also preferred that the air flow is insufficient to cause entanglement or looping of the filaments comprising a filamentary yarn. However as continuous filamentary yarns to be treated have only a small degree of twist or none at all the air stream has an opening effect on the yarn which allows the filaments to disengage from each other to some extent, an effect which enhances the uniformity of heat treatment as the yarn passes through the flame. Staple fiber yarns usually have a higher degree of twist to give the yarn the desired tensile strength, which twist opposes any opening effect of the air stream. As staple fiber yarns are usually heat treated to remove or reduce the number of projecting fiber ends such lack of opening is beneficial.

One type of yarn which may be very efficiently heat treated in a process according to this invention is one composed of thermoplastic continuous conjugate filaments or of conjugate filaments in staple fiber form. Such filaments, which are composed of two or more components arranged in contiguous fashion either sideby-side or as an eccentric sheath and core along the length of each filament, will have an inherent tendency to contract into crimped form on heating if, as is usual, the components have a different shrinkage propensity.

Other types of yarn, which have an inherent retraction tendency and which may be advantageously treated in a process according to this invention, are those in which the retraction tendency is produced by asymmetric heating or cooling of the filaments comprising the yarn during their manufacture or which are composed of a mixture of high and low shrinkage filaments or fibers.

In treating yarns which are inherently retractable it is necessary to maintain the yarn in a low or substantially tensionless state during its passage, through the flame and for a period afterwards while it is still hot. This may be achieved by allowing sufficient distance between the flame and any means for collecting the treated ya'rn together with a tension barrier, such as a roll/nip roll combination operating at a peripheral speed less than the yarn speed through the flame, situated before the collection means. At higher speeds the required cooling distance may become impracticably large and we have found that a device somewhat similar to an air ejector used for entrainment of the yarn in the air stream supplied to the flame may be used. If such a device is placed some distance from the flame and is operated so that the air flow is counter to the direction of yarn movement, the device will act both as a cooling means and as a tension barrier and as such may be used in place of or in addition to a roll/nip roll combination. If the degree of relaxation in and subsequent to the flame is to be controlled it is preferred to use a roll/nip roll in addition to the air jet tension barrier as control is thereby rendered easier. Alternatively or additionally a cooler/tension barrier of the foregoing type may be positioned after the roll/nip combination.

IN THE DRAWINGS:

FIG. 1 diagrammatically illustrates a process applied to an inherently retractable yarn; and

FIG. 2 illustrates a modified process.

A yarn I is led from a supply thereof (not shown) to the yarn inlet tube 2 of an entrainment device which comprises the yarn inlet tube 2 surrounded by a chamber 3 having an inlet 4 for a supply of compressed air and an outlet yarn passageway 5 debouching from chamber 3 at a point close to the termination of the inlet tube 2' inside the chamber 3. Outlet passageway 5 extends below the chamber 3 and in this embodiment is bent so as to provide an horizontal extremity which is surrounded by a short coaxial tube 6, closed at one end, supplied at 7 with a combustible gas and terminating at an outlet in substantially the same plane as the end of passageway 5, the two parts 5 and 6 together comprising a burner. Below and some distance from the burner is a tension barrier 8 comprising a central yarn passageway 9 extending therethrough in the wall of which is an annular passageway at an angle to the longitudinal axis of the passageway 9 and in communication with a surrounding chamber 11 to which compressed air is supplied through inlet tube 12. Downstream from the tension barrier is a take-up roll 13 with a rubber covered nip roll 14 in contact therewith.

In operation a yarn 1 is drawn into the entrainment device by reason of the partial vacuum produced at the inlet of tube- 2 by the flow of compressed air past the outlet of tube'2 into the nearby inlet of passageway 5, The yarn is thus drawn into the entrainment device and carried with the stream of compressed air into the burner being carried through the central passageway thereof to meet the flame formed at the outlet by ignition of combustible gas exiting from tube 6. The yarn is uniformly heat treated in the flame and in the succeeding zone of hot combustion gases and is caused to relax by reason of the heat and the drop in yarn tension on leaving the burner. Relaxed yarn than passes into the tension barrier 8 wherein it meets a counter flow of cool air which serves both to cool the yarn and to prevent any tension from rolls 13/14 being transmitted to the relaxation zone following the burner The yarn finally passes from the rolls 13/14 to a conventional yarn collecting means (not shown).

Fluctuations in air impede combustible fluid supply pressures may give rise to some variation in heat treatment of yarn. We have found that the effect of such fluctuations may be reduced by impinging the yarn against a surface 15 (FIG. 2) positioned beyond the tip of the flame at an angle so as to momentarily impeded the movement of the yarn without allowing tension to build up. A matt chrome-plated steel surface is one such effective material. As a combustible fluid for use in this invention there may be mentioned coal or petroleum gases or volatile liquids which may be vapourized in a current of air.

In an embodiment of the invention a conjugate multifilament oriented yarn of 150 denier containing 72 filaments composed of equal proportions of two ethylene terephthalate polymers of 0.47 and 0.67 intrinsic viscosity (measured at C in solution in O- chlorophenol) arranged in side-by-side fashion is treated in apparatus as illustrated in the drawings with the exception that the tension barrier 8 is not used. The entrainment device is supplied with compressed air at the rate of 0.19 m per hour which draws yarn into the device and forwards it to the burner at a speed of 610 meters per minute. The inner tube of the burner is made of stainless steel and measures 1.08 mm inside diamet r 'th wall thickness of 0.29 mm; it 's roundei l b y a c axial gas tube of 4.8 mm bore tl'iroii g h which towns gas is passed at the rate of 0.17 m per hour. Yarn leaving the burner forms a loop of total length cm, of which 50 cm is the substantially straight portion immediately following the burner, before being taken up by the rolls 13/14 at a rate of 334 meters per minute and forwarded to a conventional winding means. A high degree of relaxation under the efi'ects of heat and low tension is thus applied to the yarn resulting in a highly crimped bulky product wherein the crimps are of helical form.

What we claim is: i

1. A process for the uniform heat treatment of yarns comprising:

providing a burner having a central passageway which terminates at an outlet; supplying a combustible fluid through a surrounding passageway terminating at the same point as .the central passageway; entraining a yarn in a stream of air and passing the yarn therewith into and through the central passageway of the burner whereby the yarn leaves the outlet at a point where the air and the combustible fluid meet; igniting the combustible fluid to provide a combustion flame; and moving the yarn in an axial direction through the flame.

2. A process according to claim 1 wherein the yarn comprises continuous filaments or staple fibers of a synthetic thermoplastic polymer.

3. A process according to claim 2 wherein the yarn comprises thermoplastic continuous conjugate filaments or conjugate filaments in staple fiber form.

4. Apparatus for the heat treatment of yarns comprising: yarn entrainment and forwarding means having a compressed air inlet and an entrainment passageway from the end of which a yarn is discharged together with a stream of the pressurized air; and fluid fuel burner means for supplying a fluid fuel in surrounding relationship to said end of said passageway and for mixing the fluid fuel with the air stream issuing from said passageway.

5. Apparatus for the heat treatment of yarns comprising a yarn entrainment device with a connecting yarn passageway to a combustible fluid burner anda fluid yarn tension barrier after the fluid burner.

6. Apparatus for the heat treatment of yarns comprising a yarn entrainment device with a connecting yarn passageway to a combustible fluid burner and means having a surface close to the burner flame against which a yarn impinges. 

1. A process for the uniform heat treatment of yarns comprising: providing a burner having a central passageway which terminates at an outlet; supplying a combustible fluid through a surrounding passageway terminating at the same point as the central passageway; entraining a yarn in a stream of air and passIng the yarn therewith into and through the central passageway of the burner whereby the yarn leaves the outlet at a point where the air and the combustible fluid meet; igniting the combustible fluid to provide a combustion flame; and moving the yarn in an axial direction through the flame.
 2. A process according to claim 1 wherein the yarn comprises continuous filaments or staple fibers of a synthetic thermoplastic polymer.
 3. A process according to claim 2 wherein the yarn comprises thermoplastic continuous conjugate filaments or conjugate filaments in staple fiber form.
 4. Apparatus for the heat treatment of yarns comprising: yarn entrainment and forwarding means having a compressed air inlet and an entrainment passageway from the end of which a yarn is discharged together with a stream of the pressurized air; and fluid fuel burner means for supplying a fluid fuel in surrounding relationship to said end of said passageway and for mixing the fluid fuel with the air stream issuing from said passageway.
 5. Apparatus for the heat treatment of yarns comprising a yarn entrainment device with a connecting yarn passageway to a combustible fluid burner and a fluid yarn tension barrier after the fluid burner.
 6. Apparatus for the heat treatment of yarns comprising a yarn entrainment device with a connecting yarn passageway to a combustible fluid burner and means having a surface close to the burner flame against which a yarn impinges. 